(a)[2]
State Hubble’s law, and identify any symbols you use.
(b)[2]
A star with luminosity $3.8 \times 10^{31}\,\text{W}$ lies at a distance of $1.8 \times 10^{24}\,\text{m}$ from the Earth. Calculate the radiant flux intensity at the Earth of the radiation emitted by the star.
(c(i))[2]
The star in (b) is in a distant galaxy. A spectral line in the light from this galaxy is known to have a wavelength of $486\,\text{nm}$. When this spectral line in the light from the galaxy is observed on the Earth, it has a wavelength of $492\,\text{nm}$. Explain why the wavelength observed on the Earth is different from the wavelength that the galaxy is known to have emitted.
(c(ii))[3]
Determine a value for the Hubble constant $H_0$.